Developing New Guidelines on Lyme Disease

Lyme remains challenging for many reasons, not least because the bacteria that cause the disease cannot be easily grown in the lab, like strep. Without the ability to test directly for the organism, making that diagnosis early continues to depend on clinical assessment, not on the lab.

“About 80 percent of patients who have Lyme disease will have the rash of erythema migrans, and that’s a sufficient basis to start treatment,” Dr. Meissner said, referencing the signature rash, often resembling a target, which can appear (though it doesn’t always) soon after infection with the bacteria causing Lyme.

In these situations, “blood testing is not recommended because only about a third of people will have detectable antibodies when they present with erythema migrans,” he said. “If it’s the right season, if the rash has a quality that’s consistent with Lyme disease, and a person lives in an endemic area or visited an endemic area and particularly if there was a tick attachment, then it’s a clinical diagnosis,” he said.

The highest risk season is late spring and summer, when the young (and tiny) nymphal stage ticks are active and looking for hosts; adult ticks also play a role, and can transmit the disease during the spring and fall.

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What about when parents do find a tick? First of all, Dr. Meissner said, testing the tick is not recommended. However, the length of time the tick was attached is relevant. And if you can tell that the tick is engorged, that may provide some information about whether it has been attached for long enough to make transmission a risk. Borrelia burgdorferi, the main type of spirochete bacteria that cause Lyme, live in the tick’s midgut, he said, and once the tick attaches to its host and begins its “blood meal,” it takes some time for the blood to activate the bacteria.

“The spirochete has to migrate to the mouth of the tick,” Dr. Meissner said. It then gets transmitted from tick to human by reflux, journeying out from the salivary glands as the tick is feeding on blood. “If the tick is attached for less than 36 to 48 hours, then probably there’s not enough time for the spirochete to activate and get to the salivary glands,” Dr. Meissner said. “That’s why tick checks are so important — if you can catch it before 36 hours, 48 hours, it’s less likely the spirochete will be transmitted.”

The transmission process is complicated for other reasons as well. Scientists are studying the elements in tick saliva, which contains anticoagulant that gets injected through the skin into the host’s capillaries.